There has been an ever-increasing demand for compact dielectric resonators showing a small dielectric loss (tan δ) and stable dielectric characteristics in response to the trend toward a higher degree of integration of microwave circuits. When forming a dielectric filter by means of a dielectric resonator, the characteristics required for the dielectric to be used for the dielectric resonator include (1) that it is possible to make the temperature coefficient τf of the resonance frequency show a small absolute value in order to minimize fluctuations of the characteristics relative to temperature changes and (2) that it is possible to make the Q value of resonance show a large value in order to minimize the insertion loss as a requirement to be met by the dielectric filter. Additionally, since the length of the resonator is restricted by the specific dielectric constant εr of the dielectric in the microwave frequency range that is to be used for mobile phones or the like, the specific dielectric constant εr is required to show a large value when downsizing the element. The length of the dielectric resonator is determined by referring to the wavelength of the electromagnetic wave to be used for the resonator. The wavelength λ of the electromagnetic wave that is propagated through a dielectric showing a specific dielectric constant of εr is expressed by λ=λ0/(εr)1/2, where λ0 is the wavelength of the electromagnetic wave when propagated in vacuum. Therefore, the element can be downsized more when the dielectric constant of the dielectric to be used for the element is greater.
Meanwhile, laminated dielectric resonators or the like are formed as laminated electronic parts by arranging internal conductors therein in layers and sandwiching them by means of laminated and sintered dielectric ceramics. Conventionally, noble metals such as Au, Pt and Pd are used as materials of internal conductors of such laminated electronic parts. However, from the viewpoint of cost, less expensive Ag, Cu and alloys containing Ag and/or Cu as principal ingredient are being popularly used for internal conductors. Particularly, Ag and alloys containing Ag as principal ingredient provide an advantage of improving the Q characteristic of dielectric resonators because of the low DC resistance they have and hence there is an increasing demand for such materials. However, Ag and alloys containing Ag as principal ingredient have a melting point as low as about 960° C. so that it is necessary to use any of them in combination with a dielectric material that can be sintered stably at lower temperature.
Dielectric materials obtained by adding glass as ingredient are being used as materials that satisfy the above-described requirements of dielectric characteristics in order to make it possible to sinter them at low temperature. Glass ceramics made of a composite material of a BaO—TiO2—Nd2O3 type ceramic and glass are known as dielectric materials showing a high dielectric constant (Patent Document 1: JP-A-8-239263 and Patent Document 2: JP-A-10-330161).
Patent Document 1: JP-A-8-239263
Patent Document 2: JP-A-10-330161